Al Qaeda says its top leader in Afghanistan, Mustafa Abu al-Yazid, has died, according to a group that monitors Islamist websites.

He is better known by the name Saeed (Said) al-Masri.

He is said to have argued with his al Qaeda associates about the wisdom of the September 11 2001 attacks, fearing stern reprisals from the US.

He has also claimed responsibility for several terrorist bombings and assassinations.

In May 2007, al-Yazid proclaimed himself leader of al Qaeda in Afghanistan in a video on Al Jazeera.

In the video, he promised Americans that al Qaeda troops had been training through the winter and were ready to begin a fresh summer offensive in Afghanistan.

US officials told ABC News that al-Yazid's death, if true, would be great news for the counter-terrorism effort.